FIX Remove validation for FeatureUnion from __init__ (#21954)

iofall · arisayosh · glemaitre · web-flow · commit faff01b38fec · 2022-01-31T11:20:11.000+01:00
Co-authored-by: iofall &lt;50991099+iofall@users.noreply.github.com&gt;
Co-authored-by: arisayosh &lt;15692997+arisayosh@users.noreply.github.com&gt;
Co-authored-by: Guillaume Lemaitre &lt;g.lemaitre58@gmail.com&gt;
diff --git a/doc/whats_new/v1.1.rst b/doc/whats_new/v1.1.rst
@@ -506,6 +506,11 @@ Changelog
   `__init__` but in `.fit()`.
   :pr:`21888` by :user:`iofall <iofall>` and :user:`Arisa Y. <arisayosh>`.
 
+- |Fix| :class: `pipeline.FeatureUnion` does not validate hyper-parameters in
+  `__init__`. Validation is now handled in `.fit()` and `.fit_transform()`.
+  :pr:`21954` and :pr:`21888` by :user:`iofall <iofall>` and
+  :user:`Arisa Y. <arisayosh>`.
+
 :mod:`sklearn.preprocessing`
 ............................
 
diff --git a/sklearn/pipeline.py b/sklearn/pipeline.py
@@ -991,7 +991,6 @@ def __init__(
         self.n_jobs = n_jobs
         self.transformer_weights = transformer_weights
         self.verbose = verbose
-        self._validate_transformers()
 
     def get_params(self, deep=True):
         """Get parameters for this estimator.
diff --git a/sklearn/tests/test_common.py b/sklearn/tests/test_common.py
@@ -419,7 +419,6 @@ def test_transformers_get_feature_names_out(transformer):
 
 VALIDATE_ESTIMATOR_INIT = [
     "ColumnTransformer",
-    "FeatureUnion",
     "SGDOneClassSVM",
     "TheilSenRegressor",
     "TweedieRegressor",
diff --git a/sklearn/tests/test_pipeline.py b/sklearn/tests/test_pipeline.py
@@ -518,8 +518,9 @@ def test_feature_union():
 
     # test error if some elements do not support transform
     msg = "All estimators should implement fit and transform.*\\bNoTrans\\b"
+    fs = FeatureUnion([("transform", Transf()), ("no_transform", NoTrans())])
     with pytest.raises(TypeError, match=msg):
-        FeatureUnion([("transform", Transf()), ("no_transform", NoTrans())])
+        fs.fit(X)
 
     # test that init accepts tuples
     fs = FeatureUnion((("svd", svd), ("select", select)))
